Sensitive and efficient visual evoked potential (VEP) methods for measuring visual acuity in infants have been developed in the current grant period. Experiments are proposed to extend these rapid techniques to the measurement of contrast sensitivity and motion hyperacuity. A new quantitative method for photorefraction of infants which operates over a full range of refractive errors has been validated. It is now proposed to use these techniques to study the optical, retinal and central factors involved in the normal development of visual acuity. The effects of several well-defined categories of abnormal visual experience on the development of infant acuity will also be studied. For normal infants the first objective is to measure the development of contrast sensitivity as a function of spatial frequency, which will allow a range of analyses of the factors underlying acuity development. The rate of development of different retinal regions will be addressed in comparative studies of the acuities of foveal and peripheral regions, and of nasal and temporal regions. Acuity measured by the VEP will be compared directly using identical stimuli and scoring criteria, to determine whether the VEP measures an earlier level of visual processing than is available to behavior in infants, with a different developmental time course. Abnormal visual experience will first be studied in premature infants to determine the relative importance of early visual exposure and maturational factors in the growth of visual acuity. The amblyogenic effects of visual deprivation in the first year of life will be estimated by the measurement of grating acuity and motion hyperacuity in infants screened for astigmatism and anisometropia. Finally, a double-blind comparison of the detection of amblyopia in infants by clinical assessment and by VEP acuity measurement will quantify the clinical utility of the VEP methods.